Thousands of patients, including many young children, suffer extensive visual loss from hereditary retinal degenerations. In this project alone, over 1,000 patients and their families with pigmentary retinal degenerations are on file. At present no treatment is known for practically all types. Many of these conditions are described under the general heading of hereditary retinitis pigmentosa, which undoubtedly represents the end stage of many gene defects. Some progress has been made in separating and understanding the different genetic types on the basis of the abnormal electrophysiological responses in young patients. In some cases, electroretinographic (ERG) testing can be used to establish the diagnosis years before abnormalities become visible with the ophthalmoscope. At present ERG testing affords some estimation of prognosis and aids in genetic typing. Particular attention has been given to studying blue cone system abnormalities in these young patients. In addition to studies on human retinitis pigmentosa, this project is concerned with laboratory animal models that simulate characteristics of the human retinal degeneration. The cone ERG abnormalities that exist in some patients with hereditary retinal degenerations have been reproduced in the ERGs of cats which develop a retinal degeneration when fed casein as the only source of protein with a dietary induced retinal degeneration. These investigations have led to studies of the effects of some amino acids on retinal function in the cat. Electrophysiological responses have been correlated with biochemical and ultrastructural changes in the retinas of these animals. These results are also being compared with the effects on retinal function of other dietary deficiencies (Vitamin A) and known retino-toxic drugs (iodoacetate, etc.)